Cooling systems generally comprise a condenser coil, a receiving vessel for the condensed liquid from the condenser coil, an expansion valve, an evaporator coil, and a compressor. The compressor is connected to the condensor coil. In addition, such a cooling system includes a defrost mechanism for the evaporator coil since the moisture that tends to accumulate thereon turns to ice during operation and would, in time, build up to a degree that would make the cooling system almost totally inefficient, if not inoperable.
Improvements over the simplest cooling system briefly described above have included using multiple compressors, rather than only one, and alternating their use in accordance with demand so as to use only enough compressor capacity sufficient for the demand and so as to minimize wear on the compressors. Such an energy efficient system is shown and described in co-pending U.S. patent application Ser. No. 257,113, filed Apr. 24, 1981, by the same inventor as the present application. The system of application Ser. No. 257,113 represents a technique for achieving more efficient operation through the use of a single highest fixed "cut in" and a single highest fixed "cut out" operating suction line pressure while insuring adequate temperatures in the refrigerated spaces served by the refrigeration system.
In the past, the cycling of stages of a multiple-stage refrigeration or cooling system has been principally accomplished by setting each stage at a successfully lower "cut in" and "cut out" pressure of the refrigerating fluid flowing in the suction line from the evaporator coil to the compressor(s) or cooling stages. The use of successfully lower "cut in" and "cut out" pressure ranges for each cooling stage results in an average pressure which is lower than the mean pressure of the pressure differential between the "cut in" and "cut out" pressures of the highest stage. Various mechanical and electromechanical systems have been devised to attempt to solve this problem, primarily utilizing the successively lower pressure ranges for each successive cooling stage as described above.
The invention of application Ser. No. 257,113, briefly stated, involves an apparatus and method of controlling the capacity of a multiple compressor refrigeration system. The invention first establishes a selected cooling stage "cut-in" and "cut-out" suction line pressure for the system. Secondly, the system determines when the suction line pressure is equal to either of these pressures, and based on this determination, controls the selection of the appropriate capacity for the system to achieve an average operating suction line pressure between the selected single highest "cut-in" and single highest "cut-out" pressures.
The system described herein is another way or technique for increasing the efficiency of many cooling systems, and may be used independently or with the system described herein and in application Ser. No. 257,113 to achieve a cummulative system efficiency increase.
It is not unusual for the same compressor (or system of compressors) to be commonly piped in a cooling system which employs more than one evaporator coil. The reason for this is that the capacity of the system is sufficiently designed for cooling a given overall area; however, some of this area is compartmentalized separately from the rest of this area. Moreover, it is commonly desirable to reduce the temperature in one area to a lower temperature than is required for another. By example then, if one area is smaller in size than another and both are cooled in the same manner by similar evaporator coils, then the smaller area will be cooled at a lower temperature than the larger of the areas.
Rather than have two completely different systems when there are two or more separate areas to cool, such systems having duplicate compressors, duplicate condensor coils, duplicate condensor fluid vessels, and the like, it is less expensive to have one system with these common components commonly-piped, usually in parallel rather than in-line, with separate evaporator coils only. Although separate coils are commonly employed in respective separate compartments, it is also usual for separate coils to be used for a common large area, where one coil is used, for example, in one room and another coil is used in a second room, one room being kept at a lower temperature than the other.
It is also known that compressors can be operated to raise the pressure in a cooling system to warm the area cooled by an evaporator coil as well as to lower the pressure to cool the area cooled by an evaporator coil. The system to be described hereinafter includes this capability.
Therefore, it is an object of the present invention to provide an improvement for optimizing the pressure control of a cooling system having at least two commonly-piped evaporator coils.
It is another object of the present invention to provide an improvement for providing pressure control to a cooling system wherein the further away from a norm temperature an area may be, e.g. a temperature set point, the more rapid will be the rate of adjustment of pressure.